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From: NASANews@hq.nasa.gov
Date: Thu, 26 Mar 1998 15:28:26 -0500 (EST)
Fwd Date: Fri, 27 Mar 1998 19:07:38 -0500
Subject: NASA Press Release re: 'Nars Gloval Surveyor'

Douglas Isbell
Headquarters, Washington, DC
March 26, 1998
(Phone: 202/358-1547)

Diane Ainsworth
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-5011)

RELEASE: 98-50

MARS GLOBAL SURVEYOR TO ATTEMPT IMAGING OF FEATURES OF PUBLIC INTEREST

     NASA's Mars Global Surveyor spacecraft is about to begin
a summer-long set of scientific observations of the red
planet from an interim elliptical orbit, including several
attempts to take images of features of public interest
ranging from the Mars Pathfinder and Viking mission landing
sites to the Cydonia region.

	     The spacecraft will turn on its payload of science
instruments on March 27, about 12 hours after it suspends
"aerobraking," a technique that lowers the spacecraft's orbit
by using atmospheric drag each time it passes close to the
planet on each looping orbit.  Aerobraking will resume in
September and continue until March 1999, when the spacecraft
will be in a final, circular orbit for its prime mapping mission.

     It will not be possible to predict on which orbit the
spacecraft will pass closest to specific features on Mars
until Global Surveyor has established a stable orbit and
flight controllers are able to project its ground track. This
process should be completed in the next few days.  The exact
time of observations and the schedule for the subsequent
availability of photographs on the World Wide Web are
expected to be announced early next week.

     "Global Surveyor will have three opportunities in the
next month to see each of the sites, including the Cydonia
region, location of the so-called 'Face on Mars,' " said
Glenn E. Cunningham, Mars Global Surveyor project manager at
NASA's Jet Propulsion Laboratory, Pasadena, CA.  "The sites
will be visible about once every eight days, and we'll have a
30- to- 50-percent chance of capturing images of the sites
each time."

     Several factors limit the chances of obtaining images of
specific features with the high-resolution mode of the camera
on any one pass.  These factors are related primarily to
uncertainties both in the spacecraft's pointing and the
knowledge of the spacecraft's ground track from its
navigation data.  In addition, current maps of Mars are
derived from Viking data taken more than 20 years ago.  Data
obtained by Global Surveyor's laser altimeter and camera
during the last few months have indicated that our knowledge
of specific locations on the surface is uncertain by 0.6 to
1.2 miles (1 to 2 kilometers). As a result, the locations of
the landing sites and specific features in the Cydonia region
are not precisely known.

     	In addition, the Mars Pathfinder and Viking landers are
very small targets to image, even at the closest distance
possible, because they are the smallest objects that the
camera can see.  The Cydonia features, on the other hand, are
hundreds to thousands of times larger and the camera should
be able to capture some of the features in that area.

     Global Surveyor's observations of the Viking and
Pathfinder landing sites will provide scientists with
important information from which to tie together surface
observations and orbital measurements of the planet.  Data
from landing sites provide "ground truth" for observations of
the planet made from space.

	     As for the "Face on Mars" feature, "most scientists
believe that everything we've seen on Mars is of natural
origin," said Dr. Carl Pilcher, acting science director for
Solar System Exploration in NASA's Office of Space Science,
Washington, DC.  "However, we also believe it is appropriate
to seek to resolve speculation about features in the Cydonia
region by obtaining images when it is possible to do so."

     Information about Viking observations of the Cydonia
region and a listing of those images are available on the
World Wide Web at:

http://www.hq.nasa.gov/office/pao/facts/HTML/FS-016-HQ.html

     New images of the landing sites and Cydonia region taken
by Mars Global Surveyor will be available on JPL's Mars news
site at: http://www.jpl.nasa.gov/marsnews and on the
Global Surveyor home page at http://mars.jpl.nasa.gov .
These sites will also carry detailed schedules of the imaging
attempts once they have been determined.  Images will also be
available on NASA's Planetary Photojournal web site at:
http://photojournal.jpl.nasa.gov .

    So far in the aerobraking process, Global Surveyor's
orbit has been reduced from an initial 45-hour duration to
less than 12 hours.  During the aerobraking hiatus, the
spacecraft will be orbiting Mars about once every 11.6 hours,
passing about 106 miles (170 kilometers) above the surface at
closest approach and about 11,100 miles (17,864 kilometers)
at its farthest distance from the planet.  The pause in
aerobraking allows the spacecraft to achieve a final orbit
with lighting conditions that are optimal for science observations.

     Mars Global Surveyor is part of a sustained program of
Mars exploration, managed by JPL for NASA's Office of Space
Science, Washington, DC. Lockheed Martin Astronautics,
Denver, CO, which built and operates the spacecraft, is JPL's
industrial partner in the mission.  Malin Space Science
Systems, Inc., San Diego, CA, built and operates the
spacecraft camera.  JPL is a division of the California
Institute of Technology, Pasadena, CA.

			-end-